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Molecular Medicine |
From the Gazes Cardiac Research Institute and Division of Cardiology (J.G.M., Y.I, M.O., L.X., C.S.K., E.H., M.R.Z, D.R.M.), Medical University of South Carolina, and the Ralph H. Johnson Department of Veterans Affairs (J.G.M., Y.I, M.O., L.X., C.S.K., E.H., M.R.Z, D.R.M.), Charleston, SC, and the Institute of Molecular Medicine and Genetics (S.V.K., S.J.C.), Medical College of Georgia, Augusta.
Correspondence to Donald R. Menick, PhD, Gazes Cardiac Research Institute, Medical University of South Carolina, 114 Doughty St, Room 203, PO Box 250773, Charleston, SC 29425. E-mail menickd{at}musc.edu
The NCX1 gene contains three promoters (H1, K1, and Br1), and as a result of alternative promoter usage and alternative splicing, there are multiple tissue-specific variants of the Na+-Ca2+ exchanger. We have proposed that for NCX1, the H1 promoter regulates expression in the heart, the K1 promoter regulates expression in the kidney, and the Br1 promoter regulates expression in the brain as well as low-level ubiquitous expression. Here, using a transgenic mouse model, we test the role of the DNA region including -1831 to 67 bp of intron 1, encompassing exon H1 of the feline NCX1 gene (NCX1H1). The NCX1H1 promoter was sufficient for driving the normal spatiotemporal pattern of NCX1 expression in cardiac development. The luciferase reporter gene was expressed in a heart-restricted pattern both in early embryos (embryonic days 8 to 14) and in later embryos (after embryonic day 14), when NCX1 is also expressed in other tissues. In the adult, no luciferase activity was detected in the kidney, liver, spleen, uterus, or skeletal muscle; minimal activity was detected in the brain; and very high levels of luciferase expression were detected in the heart. Transverse aortic constrictionoperated mice showed significantly increased left ventricular mass after 7 days. In addition, there was a 2-fold upregulation of NCX1H1 promoter activity in the left ventricle in animals after 7 days of pressure overload compared with both control and sham-operated animals. This work demonstrates that the NCX1H1 promoter directs cardiac-specific expression of the exchanger in both the embryo and adult and is also sufficient for the upregulation of NCX1 in response to pressure overload.
Key Words: Na+-Ca2+ exchanger pressure-overload hypertrophy transgenic mice
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